System for controlling vapor pressure in fuel supply tanks



Dec. 31, 1940.

R. F. ENSXGN ETAL SYfi'TEM FOR CONTROLLING VAPOR PRESSURE IN FUEL SUPPLYTANKS Filed Nov. 18, 1938 ROY F. ENSIGN HENRY N.WADE

IN l E N TORS v A OR/VEY Patented Dec. 31, 1940 SYSTEM roa CONTROLLINGVAPOR. PRES- some IN FUEL SUPPLY TANKS Roy F. Ensign, San Marino, andHenry N. Wade, Los Angeles, Calif., assignors to Parkhill-Wade, LosAngeles, Calif., a. corporation of California Application November 18,1938, Serial No. 241,172

3 Claims.

The invention pertains to the art of supplying highly volatile fuels,such as a mixture of propane and butane, to internal combustion enginesmounted in motor vehicles.

ture of the tank and its contents is 110 F. The

vapor pressure data for propane shows that the pressure in the tankunder these circumstances will be 214 pounds per square inch absolute.Assuming that the fuel selective device is set to 5 The object of theinvention is to maintain permit withdrawal of vapor only from the tank 5the contents of the fuel tank at a substantially for all pressures above100 pounds? per square constant pressure, at least so long as thecominch absolute the fuel withdrawn from the tank. position of thecontents remains unchanged. will be taken from the vapor space onlyuntil Systems of truck and bus propulsion using the pressure hasdeclined to this set pressure.

'10 propane and butane as fuel cannot use float The'first withdrawal ofvapor will naturally refeed carburetors, as these fuels boil belowordiduce the pressure-in the vapor space, since the nary atmospherictemperature, but are provided vapor and liquid are assumed to be inequilibrium with means for vaporizing the stream of fuel with each otherat the given temperature. This passing toward the engine and formetering it in reduction of pressure will cause the liquid in the vaporform. These devices have no part in the tank to boil, tending tomaintain the pressure 15 present system and need not be described, butit in the tank constant; however, the act of boilis essential to theunderstanding of the invention ing the liquid requires the surrender ofheat by to bear in mind that the stream of fuel may the liquidequivalent to the latent heat of vaporpass to the vaporizing deviceeither as a liquid ization of the liquid boiled away; under the streamor as a stream of vapor already formed, initial conditions specified,this latent heat for 20 and that the two states may alternate withoutpropane amounts to about 140 B. t. u. per pound requiring any adjustmentof the vaporizing and of liquid vaporized. The removal of this heatmetering devices to compensate for the change from the liquid naturallylowers the temperature of state. of the remaining liquid, andconsequently re-' Propane and butane, as is well known, develop ducesthe vapor pressure within the tank. This 25 very high vapor pressureswhen heated to superprocess of cooling by vaporization continues tillatmospheric temperatures. The fuel tanks of the pressure has beenreduced to the set point heavy vehicles are usually mounted on the under0f the fuel selective device; the vapor pressure side of the vehiclebody when they are exposed curve for propane indicates that the setpressure to heat radiated from the road surface and are of 100 poundswill be reached at a temperature 3 often surrounded by hot air from theengine. of about 56 F. At this point the fuel selective Under such'circumstances, during hot weather, device will close off the outletfrom the vapor fuel tank temperatures as high as 120 to 130 space in thetank, simultaneously opening the Fahr. have been observed. These hightemperanormal liquid fuel outlet.

tures produce correspondingly high vapor pres- If the heat input to thetank through radiation 35 sures in the fuel tank, causing waste of fuelor contact with hot air continues; the fuel sethrough the operation ofthe safety relief valve, lector will take up a floating position, suchthat interfere with the accurate metering of the fuel just enough vaporis withdrawn along with the supply to the engine, and make refilling ofthe liquid fuel to maintain the tank pressure at the 40 tank diflicultby reason of the high pressure to point for which the selector is set. I40 be overcome by the charging pump. The fuel selective mechanism maytake var- We obviate all of these difliculties by the genious forms, ofwhich two are illustrated in the eral method of withdrawing the enginefeed accompanying drawing. In this drawing: stream from the fuel tank inthe liquid form so Fi 1 i s i a dia rammatic manner long as the pressurein the tank does not 'exan assembly of apparatus in which the selection45 ceed a predetermined value, and withdrawing between liquid and vaporin response to pressure vapor from above the liquid level in the tankchangeswithin the tank is performed by asingle whenever this value isexceeded. This object is valve; most readily accomplished through theagency of Fig. 2 illustrates a form of the invention in the automaticfuel selective .valve mechanisms which the'selection is effected by twocooperat- 0 which will later be described. ing valves;

The theory of the method is as follows: Fig.3 is a; detail of one formof the-selecting Assume for illustration that the fuel tank is valve. l3of Fig; 1,,and, 1- g filled with pure propane, and that the tempera-Fig. 4 is a detail of. an alternative form of selecting valve. 55

' to prevent its being brought into operation.

A selecting valve I3 is connected with the top and the bottom of tanklll by pipes l4 and |5.

As these connections are located, pipe M can withdraw only vapor andpipe [5 can withdraw only liquid from the tank. The fluid discharged bythis valve passes through a pipe l6 to any.

vaporizer I! in which it is heated to the vaporiz ing temperature bymeans of hot water, steam, or other heated fluid, and is then passed tothe engine or other point .of utilization through pipe I8.

Referring now to Fig. 3, valve [3 may consistof a housing in twosections 20 and 2| bolted together and parted by a flexible diaphragm22. The upper section encloses a spring 23 bearing on the upper surfaceof the diaphragm, the pressure exerted by this spring being adjustableby means of screw 24.

The lower section is projected downwardly to form a pct 25 within whichare formed annular valve seats .26 and 21, facing in oppositedirections. To the diaphragm is attached a valve stem 26 carrying twovalve discs 29 and 30, so spaced that when one of thediscs is on itsseat the other is spaced from its seat. Pipe I4 is connected into thepot above valve seat 26; pipe [5 is connected below valve seat 21, andpipe I6 is connected between the two valve seats. I

The space above valve seat 26 and below dia-' phragm 22 being at alltimes in communication with the vapor spaces in tank I0 through pipe M,the operation of the assembly shown in Figs. 1 and 3 is as follows. Wewill assume, as an illustration, that the upward force exerted by thevapor just balances the downward thrust of the spring when the vaporpressure in the tank is pounds per square inch. In this position theupper valve 26 is just closed and the lower valve 21 is wide open.Liquid only now flows from the tank through pipe l5, valve 21, and pipeI6 to the vaporizer ll or other apparatus for utilization of the fuel.

Now assume that the pressure on the fuel tank, due to increase inatmospheric temperature or other possible causes, increases to say 80pounds per square inch. The area of diaphragm 22 and the force constantof the spring 23 are so selected that the stem 28 moves upwardly,closing lower valve 21 against its seat and simultaneously opening uppervalve 26., It is obvious that under these changed conditions the fuelrequirements are fuel tank, the liquid connection being completely shutoff. This flow of vapor continues until the temperature of the fuel tankhas been reduced suiliciently to lower the pressure to the pointwhich-restores the valves to their initial or normal position.

It is obvious that in the event external heat is applied continuously tothe fuel tank, the system will'arrive at a floating position, in whichupper valve 26 is just enough opened to allow such quantity of vapor topass as will keep the tank in thermal equilibrium.

Fig. 2 shows another form of the invention, applicable to prevalenttypes of stationary installations. 'I'he'fuel tank I0 is shown asbefore,

with vapor line H and liquid line 15 leading from it. Liquid line I5passes first to a vaporizer I 7, heated by hot water, steam, or someother method, and capable of vaporizing the liquid under the fuel tankpressure. Valves 3|, 32, and 33 are automatically actuated by pressureresponsive devices indicated at 3m, 32a, and 33a, respectively. Pressurereducing valve 3| is provided to reduce the pressure from that in thefuel tank to the normal distribution system pressure, say 5 pounds persquare inch. Valve 3| would ordinarily be a normally open diaphragmvalve of conventional type, which is closed by increasing pressure onthe diaphragm. a

The pressure in the fuel tank is prevented from rising above apredetermined point by the cooperative action of valves 32 and 33 invapor line H, and valve 3| in the liquid line l5. Valve 32 is a normallyclosed diaphragm valve of conventional type, which is opened byincreasing pressure on the diaphragm. Valve 33 is 8. normally opendiaphragm valve which is closed by increasing pressure on the diaphragm.For the sake of illustration, valve 32 is set to open at, say 70 poundsper square inch gauge, and valve 33 is set to close at, say 7 pounds persquare inch. Under normal operation, with less than 70 pounds pressurein the fuel tank, the pressure on the fuel delivery line 16 ismaintained constant at 5 pounds by the operation of valve 3|. Since thispressure is less than the 7 pounds set pressure of valve 33, this valvenormally stands open. However, under these conditions, no flow occurs inline H, since the pressure in the fuel tank is lower than the 70 poundspressure at which valve 32 is set to open.

Now assume that the pressure in the fuel tank is increased to, saypounds per square inch, valve 32 immediately opens, and, since valve 33is already open, vapor passes through pipe 34 into the delivery line I8.Assuming that the demand on the delivery line remains approximatelyconstant, this delivery of additional vapor through valve 33 builds upthe pressure in the delivery line to 7 pounds per square inch, thepressure at which valve 33 is set to close. Since this pressure of 7pounds is higher than the 5 pounds set pressure of valve 3|, this valvecloses, shutting oif the utilization of fuel from the liquid side of thefuel tank and causing all oi.- the fuel demand to flow from the vaporspace in the fuel tank. Such flow continues until the pressure in thefuel tank is reduced to the 79 pounds set pressure of valve 32, whenthis valve closes and normal fuel supply conditions are resumed throughthe liquid linevapqrlzer and valve 3!.

The valve shown in Fig. 4 is a simpler device than the valve of Fig. 3,accomplishing its effect of selection by the aid of gravity and thusrequiring only one seat and disc. It is useful when there is sufficienthead room to permit it to be inserted directly into the top of tank III,the only position in which it is functional.

Referring to Fig. 4, 40-40 is a fragment of the upper side of tank l6;ll is a body having two vertical passages 42 and 43. Passage 42terminates just insidethe shell of the tank and thus communicates onlywiththe vapor space within the tank, while passage 43 is continued to apoint near the bottom of the tank by a drop pipe 44 and thuscommunicates only with the liquid space.

.Passage 43 continues without obstruction into the outlet is throughwhich the fuel flows to the point of utilization. Passage l2 terminateswithin the valve body but communicating with the upper part of passage43 (and therefore with outlet l8) through a port 45. In'this port isformed a valve seat 46 to which is fitted a valve disc 41-, this discbeing in the form of a piston sliding in a lateral extension 48 of thevalve body. Bearing against the rearward face of this piston is aSylphon bellows 49 and an open coil spring 50, both held in position bya screw cap 5|.

So long as the vapor pressure in passage 42 is insufficient to lift disc41 from its seat, the vapor pressure within the tank causes liquid toflow through pipe 44 and passage 43 to the point of utilization. Whenthe pressure in passage 42 exceeds the pressure for which spring 50 isset, the bellows collapses, disc 41 is lifted from seat 46, and vaporflows through port 45 into passage 43 and outlet [8. So long as thisvalve remains open, the hydrostatic head in pipe 44 prevents the flow ofliquid into passage 43. If desired, an extension 52 from disc 4'! may becontinued through cap 5| and provided with a lifting lever 53 foropening valve 41 manually. This is convenient for starting cold engines.

While the invention has been described with sole reference to thesupporting of fuel to automotive engines, it will be understood that itis equally applicable to stationary engines,- to industrial applicationutilizing volatile liquids as a source of clean gas fires, and toheating and cookin'g installations,.in fact to any tankof volatile fuelexposed to variable temperatures.

We claim as our invention:

1. Apparatus for protecting tanks of volatile fuel against excessivepressure, comprising: channels communicating with respectively thevaporspace and the liquid space within said tank; a valve body communicatingwith both said channels; a movable element acted on by the pressure insaid vapor channel; resilient means restraining the movement of saidelement; individual valves arranged across said channels;

means actuated by movementof said movable element to open only the vaporvalve whenthe vapor pressure exceeds a predetermined maximum and to openonly the liquid valve when the vapor pressure falls below said maximum,and a common outlet channel to receive the .fluid pass ing througheither of said valves.

2. Apparatus for protecting tanks of volatile fuel against excessivepressure, comprising: channels communicating with respectively the vaporspace'and the liquid space within said tank; a body located above saidtank, containing portions of said two channels, provided with an outletconnection communicating with saidliquid channel, and provided with aport connecting said channels with one another; and a movable valvemember adapted to maintain said port closed while the vapor pressurewithin said tank is below a predetermined limit and to open said portand admit vapor at substantially full tank pressure to said liquidchannel when said vapor pressure rises to above said predeterminedlimit.

3. Apparatus for protecting tanks of volatile fuel against excessivepressure, comprising: channels communicating with respectively the vaporspace and the liquid space within said tank; a valve body communicatingwith both said channels and with an outlet channel; a movable elementacted on by the pressure in said -vapor channel; resilient meansrestraining the movement of said element; and a. valve member, actuatedby said movable element, arranged to maintain said vapor channel closedwhile said vapor pressure is below a limit predetermined by the strengthof said resilient means and to open said vapor channel and prevent flowof .liquid in said liquid channel when said vapor pressure is above saidpredetermined limit.

ROY F. ENSIGN. HENRY N. WADE.

